Question

I have a hard time telling what charge is on the elements in the transition groups. I didn't know that Cu is 2+. How do I know this? Can I use hunds rule and use electrons filling up the p orbital to figure this out? Or do I need to always look at the connecting compound or element connected to these transition metals? I never know what the charge of an ion is in chemisty. I need some advice-

Answer 1

The transition elements can be tricky. As a rule, the maximum oxidation state is equal to the group number up to 7B: Sc+3,Ti+4,V+5,Cr+6,Mn+7, and is +3 for Fe, Co and Ni, and then +2 for Cu and Zn. Most will exihibit a number of oxidation states less than the maximum, with notable exceptions, e.g. Sc is always +3, Ti strongly prefers +4, +1 is generally rare except for Cu, and Zn is never anything other than +2. In the case of true ions, i.e. the atom actually has that charge, +2 and +3 are generally common, excepting Sc and Ti, and Cu which never does +3. Some of these generalization apply to the 2nd and 3rd transitions series, but not all. Generally in lower rows the higher oxidation states are more common.

The situation is tricky because the d electrons are quite close in energy to the s electrons, at least early in each transition series, so some of them can be ionized (or at least shared with other atoms), depending on how strongly oxidizing the other atom is, and that gives the transition metals multiple valences. In some cases it's pretty easy to understand: for example Zn is [Ar]3d10,4s2 so of course it's just going to lose those 2 4s electrons to be +2, and since the 3d shell is complete, it's going to be hard to pull off any more electrons. Sc is [Ar]3d1,4s2, so anything that can pull off the two 4s electrons will also pull off the very well-shielded 3d electron -- so Sc is always +3.

You can rationalize almost all of the common oxidation states of the transition elements based on their electron configuration, but simple rules are not easy to come by.